The present invention refers to an illumination device or exposure device for producing models, such as reticles and masks, used for manufacturing electronic elements, or for direct illumination of wafers and substrates during the photolithographic steps required for production, or for direct illumination of structures including light-sensitive layers, said illumination or exposure device comprising a light source and a pattern generator.
The present invention especially deals with the production of models, reticles and masks, or with direct illumination in the micrometer range in the fields of semiconductor production, the production of integrated circuits, hybrid production and the production of flat screens as well as similar production methods in the case of which illumination processes are used. The present invention especially concerns an illumination device, which is adapted to be used for direct illumination of semiconductor wafers in the field of semiconductor production and for direct illumination of substrates in the field of hybrid and bonding technology.
For the production of reticles, which are illumination templates for the photolithographic production of circuits, as well as for the production of masks and for direct illumination of semiconductor products, electron beam writers, laser beam units and optical pattern generators including a laser light source or a mercury-vapour lamp are used. Optical pattern generators according to the prior art produce the desired structures by carrying out successive, individual illuminations of rectangular windows, which are defined by mechanical rectangular shields. The complexity of the structure to be produced determines the number of illumination rectangles required, and said number, in turn, determines the writing time or the exposure time for the structure. The accuracy of the structures which can be produced by these known pattern generators is, in turn, limited by the accuracy of the mechanical rectangular shields used.
In the case of laser beam units according to the prior art, the surface to be illuminated is rastered by a laser beam. The writing speed or illumination speed of such laser beam units is limited due to the serial data flow required for the rastering process. In addition, such laser beam units necessitate high mechanical-optical investments.
The electron beam units employed in the prior art can only be used for the illumination of electron-sensitive, special photoresist systems, and, in comparison with the above-described laser beam units, they additionally require the use of a high-vacuum technique. It follows that electron beam units necessitate very high capital expenditure and operating costs.
The technical publication B. W. Brinker et al, "Deformation behavior of thin viscoelastic layers used in an active, matrix-addressed spatial light modulator", Proceedings of SPIE 1989, vol. 1018, already discloses the use of a reflective optical Schlieren system including an active, matrix-addressed, viscoelastic surface light modulator for the purpose of producing television pictures or for the purpose of image display. This surface light modulator includes a permanent light source whose light falls vertically onto the surface of the surface light modulator through an appropriate optical system. Surface areas of the surface light modulator are adapted to be deformed in response to addressing of control electrodes so that the light falling onto the surface will be reflected as diffracted light in the case of addressed surface elements and as undiffracted light in the case of non-addressed surface elements. The undiffracted light will be returned to the light source, whereas the diffracted light will be used via the optical Schlieren system for image production on the television screen or on an image display area.
The company publication of the firm of Texas Instruments, JMF 008:0260; 10/87, discloses a surface light modulator whose reflective surface consists of a plurality of electrically addressable, mechanically deformable reeds.
The older, not prepublished international patent application now U.S. Pat. No. 5,296,891 describes an illumination device for producing models or for the direct illumination of electronic elements, said illumination device comprising a light source and a pattern generator. The pattern generator is provided with an optical Schlieren system and with an active, matrix-addressable surface light modulator having a viscoelastic control layer with a reflective surface. Between the Schlieren lens and the projection lens of the Schlieren system, a mirror device is arranged, which fulfills preferably a double function, said mirror device being used for deflecting the light coming from the light source onto the surface light modulator and serving as a filter device for filtering out undiffracted, reflected light. The Schlieren lens is arranged close to the surface light modulator. A positioning table, which is adapted to be displaced, serves to receive thereon the model or the electronic element. In this illumination device, the introduction of light from the light source via the mirror device onto the surface light modulator is effected with the aid of a focussing means, which is arranged in the beam path in front of the mirror device and which focusses the light coming from the light source onto the mirror device. In other words, a virtual point light source for illuminating the surface light modulator is necessarily produced at the location of the mirror device when this illumination device is used, and this will result in limitations with respect to the structural design of the illumination device and the arrangement of its mirror device as well as of its filter device.
U.S. Pat. No. A 4,675,702 discloses a surface exposure device, which can be used e.g. for exposing photosensitive films and which may be constructed as a "photoplotter". This exposure device comprises a light source for generating an essentially parallel bundle of light falling through a controllable light matrix valve, which can, for example, consist of a liquid crystal layer, whereby areas of the photosensitive film which are not to be exposed will be defined.
U.S. Pat. No. A 4,728,185 deals with a Schlieren imaging system, which can be used with light modulators in an optical printer. The light valves themselves can be constructed as electronically addressable surface light valves. The known illumination device is arranged in such a way that only the parts of the bar-shaped light modulator which are addressed will be imaged on a photosensitive layer.
U.S. Pat. No. A 4,592,648 discloses an illumination system which is used for forming an image of a model on a light-sensitive layer on a semiconductor material and which is provided with a displaceable positioning table.